The field of this invention is safety apparatus for underwater divers for use in helium or other gas reclamation, and in particular, safety apparatus preventing a dangerous outflow of exhaust gas from the diver's helmet or other such habitat.
In recent years, the level of offshore oil and gas exploration and production has substantially increased the necessity of diver utilization at significant water depths, such as 150 feet and below, to install and repair equipment. It has been a common practice to utilize a diver breathing gas mixture consisting essentially of nitrogen and oxygen; but, at deeper depths, such as 150 feet and below, the utilization of nitrogen in the breathing mixture creates the most serious problem of nitrogen narcosis caused by the absorption of nitrogen into the body. Nitrogen narcosis is best avoided by reducing nitrogen in the breathing mixture. Helium has been found to be a desirable inert gas for use in a helium-oxygen breathing mixture which is readily usable by divers at such significant depths without the tremendously high probability of dangerous absorption into the body. However, helium is a rare gas and is thus very expensive by comparison to nitrogen.
When using nitrogen-oxygen breathing mixtures, it is the practice to exhaust helmet gas directly into the water surrounding the diver. However, when helium is used in a helium-oxygen mixture, it has been found desirable to recover the exhausted gas for recycling in order to reclaim the helium for further use. Helium recovery systems, such as disclosed in U.S. Pats. Nos. 3,924,616 and 3,370,585, recycle diver exhaust gas for reuse by essentially removing carbon dioxide from the exhaust gas and adding oxygen thereto while preserving the supply of helium. Such diver gas recovery systems are located either on the water surface or at a diving bell or habitat located below the water, but generally above the locus of diver activity. In diver gas recovery systems, a diver gas supply line and an exhaust gas recovery line extend from the recovery system to the diver. The pressure of the breathing gas supply flowing into the diver's helmet is equal to or slightly above the pressure of the water surrounding the diver, this is termed herein "ambient water pressure." Therefore, the pressure of the exhaust gas leaving the diver's helmet and flowing into the exhaust gas line is slightly greater than ambient water pressure or essentially equal to it. However, the pressure at the other end of the exhaust gas return line attached to the helium recovery system, such as at the water surface, is at a substantially lower pressure than the pressure of gas leaving the diver's helmet. This pressure differential between the diver's helmet and the helium recovery system may cause a dangerously fast outflow of gas from the diver's helmet and thus decompression of the helmet, which may kill the diver.
It is presently known in the art to utilize various types of mechanical valve arrangements located in the exhaust gas return line to control the flow of the exhaust gas from the diver's helmet to the diver gas recovery system. For example, U.S. Pat. No. 3,924,616 discloses a combination of a safety shut-off valve and a back-pressure regulator valve mounted in the exhaust gas return line to maintain a desired pressure within the diver's helmet. U.S. Pat. No. 3,968,795 discloses the location in series of a normally open fail-safe valve and an exhaust control valve for maintaining helmet pressure within predetermined limits relative to ambient water pressure. Should the exhaust control valve fail in the device disclosed in U.S. Pat. No. 3,968,795, the fail-safe valve is designed to close to cut off any exhaust flow and thus prevent pressure within the helmet falling to a dangerously low level. U.S. Pat. Nos. 3,802,427 and 3,370,585 also disclose subject matter relating to the control of breathing and/or diver gas recovery systems. U.S. Pat. No. 3,467,094 relates to a bladder-type of control device for preventing oxygen dumping in a decompression chamber.